I would buy a compression tester they are only like $25-30. It can rule out alot of things more quickly than tring to doing ecu code diagnostics.

Also if you are running rich it could be just a AFM adjustment you are running a air intake am I right?
It could be even loose air intake fittings as well a gap will cause weird idling and stuff..
It's not always a faulty O2 sensor.
You can definately change it out and see what happens but you might try leaning out the AFM. Don't do it too much you will get detionation.

If it is headgaskets or valves definately spend the money to have the heads and valves re-done by a machine shop it's well worth it then put a fresh set of head gaskets on.

I would suspect bad compression due to valves or headgaskets.
A good sized impact can cause all kinds of things to unseal break loose break contacts all kinds of stuff.

Hell I am on 32x11.50's I can do 80-85 in 4th and the valve gaps and timing cam is off on 2,4,6 bank and it isn't WOT yet.

Just my 2 cents.